There has been known a sheet transport device configured to read an image on a sheet using a reading unit while transporting the sheet along a predetermined transport path.
The sheet transport device separates a plurality of sheets set on a sheet supporting surface sheet by sheet, transports a separated sheet, and reads an image on the sheet during the transporting process.
In this type of sheet transport device, a size of a sheet which can be read by the sheet transport device is set as specification in advance. In other words, a maximum sheet size and a minimum sheet size of a sheet which can be transported in the transport path is set as specifications. In many cases, the maximum sheet size and the minimum sheet size, in particular, the minimum sheet size is determined by a distance of arrangement of transport roller pairs in a transport direction which are arranged at a plurality of positions on the transport path to transport the sheet.
In other words, in many cases, there is employed a method in which a driving roller and a driven roller of the transport roller pair nip a sheet to transport the sheet. In this configuration, in order to appropriately transport a sheet, it is necessary to pass the sheet from a nip portion of the transport roller pair arranged at an upstream side of the transport path to a nip portion of a subsequent transport roller pair arranged at a downstream side. Therefore, it is necessary that the transport roller pairs are arranged within a distance allowing the passing of the sheet and the sheet is laid across at least two of the nip portions at the upstream side and the downstream side.
When a user accidentally or forcibly sets a sheet smaller than the minimum sheet size set as specifications of the device on a sheet supporting surface, performs a reading start operation, and starts the transporting of the sheet, there could be a concern, for example, that the passing of the sheet cannot be performed and the transporting of the sheet is stopped at a middle of the transport path. When the transporting of the sheet is stopped in the middle of the transport path, it is difficult to take out the sheet.